HIV - I affects human immune system and reduces the ability of immune system to fight against pathogenic infections, this condition is called as acquired immunodeficiency syndrome (AIDS). HIV is a slowly replicating retrovirus, responsible for infection throughout the world. HIV shows high genetic variability. These virus infects vital cells of the human immune system such as helper T cells (CD4+), macrophages and dendrite cells. AIDS is a chronic, potentially life-threatening condition caused by the prolonged HIV infection. There's no cure for HIV/AIDS, but there are medications that can dramatically slow the progression of the disease.